<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <!--http://localhost:8080/jdbc/html/regular/regular.html-->
    <title></title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }



        .container {
            width: 750px;
            height: 680px;
            background: rgba(86, 88, 89, 0.5);
        }


        .main {
            top:150px;/*通过相对布局计算得到的垂直居中,这种垂直居中前提条件为position: relative*/
            position: relative;
            width: 450px;
            height: 380px;
            background: rgba(255, 0, 15, 0.5);
            margin:  0 auto;/*左右居中,这里有前提条件:*/
        }


    </style>
</head>


<body>
<div class="container">
    <div class="main">main
    </div>
</div>
</body>
</html>